My 1st or 2nd grade teacher back in the mid sixties pointed out the lack of a gender neutral pronoun and that the use of they or their is perfectly acceptable.
So it's not like anyone has recently discovered this lacking part of our English language. Mostly I think it's just from those that only moderately understand the English language and can only fathom they and their as plurals instead of the ability of those words to also refer to a singular person.